1. Field of the Invention
The present invention relates generally to nuclear fuel pellet inspection and, more particularly, is concerned with a nuclear fuel pellet turning apparatus and method for facilitating surface inspection of pellets.
2. Description of the Prior Art
In a typical nuclear reactor, the reactor core includes a large number of elongated fuel assemblies. Conventional designs of these fuel assemblies include top and bottom nozzles with a plurality of elongated transversely spaced guide thimbles extending longitudinally between and connected at opposite ends to the nozzles and a plurality of transverse support grids axially spaced along the guide thimbles. Also, each fuel assembly is composed of a multiplicity of elongated fuel elements or rods transversely spaced apart from one another and from the guide thimbles and supported by the transverse grids between the top and bottom nozzles.
The fuel rods each contain fissile material in the form of a plurality of generally cylindrical nuclear fuel pellets maintained in a row or stack thereof in the rod. The fuel rods are grouped together in an array which is organized so as to provide a neutron flux in the core sufficient to support a high rate of nuclear fission and thus the release of a large amount of energy in the form of heat. A liquid, coolant is pumped upwardly through the core in order to extract some of the heat generated in the core for the production of useful work.
During the manufacture of the fuel rods for the fuel assemblies, visual inspection of the nuclear fuel pellets is a key operation for the production of quality fuel assemblies. The entire cylindrical surface of the pellet is checked for dimensional quality, cracks and other defects, including chipped edges. The practice heretofore for inspecting pellet surfaces has been to provide side-by-side rows of aligned pellets on a first pellet support tray. After an operator visually inspects the exposed portions of the external cylindrical surfaces of the pellets, a second empty pellet support tray is placed upside down over the pellets loaded on the first support tray. With the two trays held together, they are manually inverted so as to transfer the pellets en masse from the first support tray to the second support tray. The operator again visually inspects the newly-exposed portions of the external cylindrical surfaces of the pellets to complete the inspection of the pellets.
This conventional practice has several drawbacks. First, the weight of the pellets and the two trays is oftentimes excessive and unacceptable from the standpoint of the capabilities of the typical operators. Second, the trays are often warped slightly, which could permit pellets to fall out during the turn-over or inverting action. Third, and more importantly, the portion of the cylindrical surface of the pellet than occurs at the horizontal midplane of the pellet cannot be effectively inspected due to the geometry of the pellet array and the overhead position of the light source. This questionable region amounts to approximately ten percent of the cylindrical surface of the pellet.
Consequently, a need exists for improvement of the manner in which nuclear fuel pellet surface, inspection is carried out so as to eliminate the problems associated with the prior art method and still further improve the quality of fuel fuel pellet inspection.